1. Field of the Invention
The present invention relates to a signal sensing device for a magneto-optic disk device, and more particularly, to a signal sensing device for sensing a tracking error signal, a focusing error signal and an information record signal in accordance with a beam reflected onto a magneto-optic disk.
2. Description of the Related Art
In an optical system of a conventional signal sensing device, a laser beam outputted from a semiconductor laser device passes through two half-mirror planes in a compound prism and is reflected onto a magneto-optic disk. A part of the beam reflected onto the magneto-optic disk is reflected by one of the half-mirror planes onto an error sensor provided for obtaining a focusing error signal and a tracking error signal. The other part of the beam is reflected by the other of the half-mirror planes and is split by a polarized beam splitter. The split beams are reflected onto data sensors provided for obtaining an information record signal recorded in the magneto-optic disk.
In the magneto-optical disk device, three kind of signals, i.e., the focusing error signal, the tracking error signal and the information record signal, must be obtained from a laser beam reflected onto the magneto-optic disk. Therefore, in the conventional device described above, one sensor is provided for sensing the error signals, and two sensors are provided for sensing the information record signal. When a sensor is provided only for sensing the error signals, however, the number of photo sensors is increased, and thus the optical system becomes complicated.